Originally Posted by pb4uski
. snip.....I'm actually building a new place right now and the exhaust hood will be along an outside wall. When I talked with my builder about venting the range hood outside he said he rarely did that. I was surprised, but he knows his stuff.
I'm not surprised. Most builders would probably prefer twisting in a few screws to install the unit on the wall, hook up 3 wires, and they are done.
No bothering to order up duct, a dampered vent cap, mounting the duct adaptor on the back, cutting a hole through drywall and exterior wall surface, assembling it sealing it properly, etc. etc.
Many vent hood units have selectable 3-way output. Vent out the back (through wall, usually with rectangular duct), vent out the top (usually round vent pipe up through cabinet above, then to vent on roof or elbow to vent out the wall), and lastly, everyone's favorite... recirculate into room by not opening up any of the above real vent knock-outs, and not inserting the block-off plate in the front grill.
Instructions with these units say that if you choose the recirculate into room mode on installation, you must use the activated carbon filter (an expensive extra cost item not supplied with the stock unit), and change it regularly.
In this house, one of my goals when I renovated the kitchen was to trash the single-speed vent hood that vented back into the room. It was worthless. When ON, it sounded like a diesel was running in the kitchen. And of course it didn't really do anything useful, so no sense running it.
I figured my chances were less than 50% that there would NOT be stud in the way to try to vent a new one out the back. Of course there was a stud, about 2/3rd's over the proposed duct space. I did not want to go out the top and through cabinets, then through the roof. And the outside soffit level precluded trying to go up and out the wall. So I opened up the wall behind the hood area and headed off the offending stud above and below where the rectangular duct would go through. Bent up my own custom duct, and drilled out bricks in the way. The drywall seams are covered up by the cabinets, and the bottom seam is covered by the vent hood unit itself.
Works great. Use it often. Lowers heat and moisture buildup in the kitchen during A/C season, which is long here. I like watching it slurp up the steam when raising a pot lid. During a recent unseasonably cold spell here in early Feb., could see steam blowing out the outside vent in a cloud, viewing from a window when DW lifted a pot lid when checking on some pasta. Looked just like a restaurant!
And when cooking any meat with grease, I like that the grease fumes are going outside, not back inside coating the room and our lungs. And yes, grease fumes do condense and leave a film inside if they are not vented outside.